Preparation of alpha-olefin block copolymers

ABSTRACT

THIS INVENTION RELATES TO THE SOLUTION POLYMERIZATION OF A-OLEFINE TO FORM BLOCK COPOLYMERS. THE POLYMERIZATION IS CONDUCTED IN THE PRESENCE OF A CATALYST COMPRISING TITANIUM TRICHLORIDE AND A LITHIUM COMPONENT.

United States Patent 3,639,515 PREPARATION OF a-OLEFIN BLOCK COPOLYMERSHugh J. Hagemeyer, Jr., and Marvin B. Edwards, Longview, Tex., assignorsto Eastman Kodak Company, Rochester, N .Y.

No Drawing. Continuation-impart of application Ser. No. 28,826, May 13,1960, which is a continuation-in-part of applications Ser. No. 615,775,Oct. 15, 1956, now Patent No. 3,067,183, and Ser. No. 668,840, July 1,1957. This application Feb. 6, 1969, Ser. No. 797,246

The portion of the term of the patent subsequent to Oct. 12, 1988, hasbeen disclaimed and dedicated to the Public Int. Cl. C08f 1/30, 15/00US. Cl. 260878 B 4 Claims ABSTRACT OF THE DISCLOSURE This inventionrelates to the solution polymerization of a-olefins to form blockcopolymers. The polymerization is conducted in the presence of acatalyst comprising titanium trichloride and a lithium component.

This application is a continuation-in-part of application Ser. No.28,826, filed May 13, 1960, which is a continuation-in-part ofapplication Ser. No. 668,840, filed July 1, 1957, now abandoned, andapplication Ser. No. 615,775, filed Oct. 15, 1956, now US. Pat.3,067,183.

This invention relates to new compositions of matter and methods fortheir preparation. More particularly, the present invention relates tosolid crystalline block c0 polymers of propylene with other oc-OlCfiIlSwhich have enhanced properties. In a specific aspect this inventionrelates to propylene polymers having superior low temperaturebrittleness properties and a novel two-stage process for theirpreparation.

It is known that OL-Olfifil'lS such as propylene can be polymerized torelatively high molecular weight solid polymers by subjecting themonomer to relatively mild conditions of temperature and pressure in thepresence of ionic catalyst mixtures. The polymerization proceduresemploying such catalyst mixtures can be carried out at temperaturesranging from below room temperature such as, for example, temperaturesof 0 C. to temperatures in the order of 250 C. and higher. Thesecatalysts are also effective at pressures from atmospheric to very highpressures in the order of 30,000 p.s.i. or higher, although only slightsuperatmospheric pressures are usually required and hence, pressures upto 1,000 p.s.i. are ordinarily employed.

However, as disclosed in U.S. Pat. 2,918,457 which issued on Dec. 22,1959, crytalline polymers of propylene, i.e., propylene polymersexhibiting crystalline structure by X-ray analysis, possess manydesirable properties, but they are not suitable for use in manyapplications because of their high brittle points. By brittle point ismeant the temperature at which the polymer exhibits brittle failureunder specific impact conditions as measured, for example, by ASTMD747-55T. As pointed out in the aforementioned patent, many of theplasticizers heretofore used with various plastic materials do notappear 3,639,515 Patented Feb. 1, 1972 ICC suitable for improving thebrittle point of polypropylene because such materials lower the tensilestrength and/or adversely atfect other physical properties of thepolymer such as the melting point, melt index and the like.

In US. 2,918,457 the brittle point of propylene polymers is improved bypolymerizing mixtures of propylene and butene-l to form copolymers inwhich there is a random distribution of each of the monomers in thepolymer chain. One disadvantage of such copolymers is that at least 7%thereof must be butene-l in order to obtain a product having abrittleness temperature below 0 C. Furthermore, random copolymercomprising propylene and another a-olefin, for example, ethylene, werefound to have brittle points in excess of 7 C. as shown at column 4,lines 8-13 of the above-mentioned patent.

It is evident, therefore, that the state of the art will be enhanced byproviding a class of propylene polymers having an improved brittlepoint. Likewise a noteworthy contribution to the art will be a methodfor the preparation of such compounds.

Accordingly, an object of this invention is to provide new propylenepolymers having low brittle points.

Another object is to provide novel copolymers comprising propylene anda-monoolefins which copolymers have low brittle points.

Still another object of this invention is to provide novel copolymerscomprising propylene and another oc-IIIOHO- olefin, for example,ethylene, which exhibit brittle points as low as 50 C.

Still another object of this invention is to provide novel propylenecopolymers containing as little as 5% of a second a-monoolefinic monomerwhich copolymers will exhibit brittle points as low as 40 C.

Still another object of this invention is to provide a novel two-stageprocess for preparing such copolymers.

Other objects will become apparent from an examination of thedescription and claims which follow.

In accordance with this invention it has been found that solidcrystalline block copolymers containing at least by weight, ofpropylene, with a different (ac-ID0110- olefin, prepared as describedhereinafter, have very low brittle points while still retaining thedesirable properties of crystalline polypropylene.

It should be understood that the block copolymers of this invention arequite different from the ordinary type of copolymer prepared heretofore.For example, it is well known that copolymers of various unsaturatedcompounds can be prepared by the simple expedient of subjecting amixture of two or more monomers to polymerization conditions as shown inUS. Pat. 2,918,457, for example. However, this type of process resultsin a copolymer having a random distribution of each of the monomers inthe polymer chain. On the other hand, the copolymers of this inventionare block copolymers and exhibit a very definite and precise arrangementof each of the polymer components in the polymer chain. The blockcopolymers of this invention can be represented as those containing apolymer chain illustrated by the formula AAAAAAAABB wherein A is thepropylene component and B is the comonomer as contrasted to the randomcopolymers of the prior art which contain polymer chains represented bythe formula AABABBA. The precise arrangement in the copolymer makes itpossible, by appropriate selection of the type and amounts of eachpolymer component as well as the polymerization conditions and ratio ofthe catalyst components, to produce copolymers having a Wide variety ofproperties in addition to the low brittle point. This wide flexibilityin properties of the copolymers of this invention is not obtained withmost of the prior art copolymers.

Also, in prior art copolymers it has often been found that the productis a blend containing large amounts or mixtures of polymers preparedfrom each of the monomers. These mixtures are, of course, quite distinctfrom the copolymers of this invention which contain the polymercomponents in a single polymeric chain. The prior art products shouldmore aptly be termed poly blends or simply mixtures of polymers. In ourinvention we find it advantageous to use no more poly-a-monoolefin inour process than can be incorporated in the polypropylene chain, theexact preferred amounts being determinable by the copolymer beingproduced and the polymerization conditions used. In this manner it ispossible to avoid the production of a poly blend instead of a truecopolymer.

The block copolymers of this invention can contain varying amounts ofeach of the polymers in a single polymeric chain. For example, thecopolymer can contain from 80 to 99% of polypropylene and from 1 to 20%of a poly-a-monoolefin. The amounts of each of the components can bevaried within these ranges to produce a copolymer having specificdesirable properties. In general, however, the block copolymers of thisinvention are characterized by molecular weights of at least 10,000, andpreferably within the range of about 15,000 to about 100,000, densitiesof at least 0.85, with densities within the range of 0.87 to about 0.92being preferred, and brittle points lower than C.

The novel copolymers of this invention are produced in a two-stagepolymerization procedure in which propylene is contacted with a solidstereospecific polymerization catalyst in the first stage and the secondmonomer is then added to the second stage to produce a block copolymercontaining at least 80% propylene and having a brittle point lower than0 C. This two-stage process can be conducted in a single reactor havingseparate reaction zones preferably separated by a baflle or otherseparation means. However, the two separate reactions forming ourprocess can also be conducted in separate reactors arranged in seriesand alternatively the entire process could be carried out in anelongated tubular reactor. The block copolymers of this invention canalso be produced batchwise by carrying out the first portion of thepolymerization with propylene and then adding ethylene or a seconda-monoolefin after a portion of the propylene, e.g. 20- 30%, has beenpolymerized. The exact amount of monomer fed to the second stage willvary widely depending upon such variables as the reaction conditionsemployed, the percent of propylene converted to polypropylene in thefirst stage, the desired molecular weight of the block copolymer andsimilar variable factors. Consequently, the amount of monomer fed, in aspecific situation, will depend upon the correlation of the severalvariable factors. However, this amount of monomer will be such that theblock copolymer contains at least 1 percent, by 7 weight, of the secondmonomer copolymerized with at least 80 percent by weight of propylene.

The catalysts which are employed in practicing this invention are animportant feature of the process and incombination with an activatortherefore. These catalysts include, for example, mixtures containing ahalide of a transition element from the 4th to the 6th subgroups of thePeriodic Table in combination with a metal of Group I-A or II oraluminum, or with an alloy of metals of Group I-A and/or II and/oraluminum, or with a halide or organometallic compound of a metal ofGroup I-A or II and/or aluminum, or with a complex hydride or a complexorganometallic compound of boron or aluminum and a metal of Group l-A orH of the Periodic Table. The Periodic Table referred to herein can befound in Langes Handbook of Chemistry, 8th edition (1952), published byHandbook Publishers, Inc. at pages 56 and 57, for example.

The transition metals included in Groups IV-B-VI-B of the Periodic Tableare exemplified by metals such as titanium, zirconium, vanadium,molybdenum, chromium, and the like. The transition metal halide catalystcomponents can be used at their maximum valence, or if desired, areduced valency form of the halide can be employed. It is preferred touse the titanium chlorides which can be in the form of titaniumtetrachloride, titanium trichloride and titanium dichloride. Examples ofother transition metal halides that can be employed in the process ofthis invention include titanium tetrabromide, titanium tri bromide,zirconium tetrachloride, zirconium tetrabromide, vanadium trichloride,molybdenum pentachloride, chromium trichloride, and the like.

Suitable activators which can be employed in conjunction with thetransition element halides include, for example, metal alkyls, metalaryls, metal alkyl halides and metal hydrides of aluminum or Groups I-Aand H as Well as the metals above. The preferred activator is a lithiumcomponent as exemplified by lithium metal, lithium alkyl, lithiumaluminum hydride, lithium aluminum alkyls, lithium borohydride, lithiumdialuminum heptahydride, and the complex reaction products containinglithium such as the product obtained by reacting lithium hydride orlithium alkyl with an aluminum alkyl or alkyl aluminum hydride, ormixtures of these in combination with a Group IV-B to VI-B transitionelement halide at a valence state of one less than maximum. Thirdcomponents such as NaF, and MgO may also be used. Such preferred hightemperature stereospecific catalysts for the polymerization of propyleneand higher alphaolefins are, for example, lithium aluminum hydride incombination with titanium trichloride, and sodium fluoride; lithiumdialuminum heptahydride in combination with titanium trichloride, sodiumtfluoride and magnesium oxide; and complex lithium containing compoundssuch as the product obtained by reacting lithium hydride or lithiumalkyl with an aluminum alkyl or alkyl aluminum hydride in combinationwith titanium trichloride.

Suitable Group I-A or II metals include sodium, potassium, lithium,zinc, and the like. The alloys, halides, hydrides, or organometalliccompounds of these metals include, for example, sodium amyl, potassiumbutyl, lithium propyl, zinc dibutyl, zinc diamyl, zinc dipropyl, ethylmagnesium bromide, sodium hydride, calcium hydride, lithium aluminumhydride, and the like. Also, the catalyst composition can contain ororgano aluminum compound such as aluminum triethyl, aluminum tributyl,ethyl aluminum dichloride, cyclohexyl aluminum dichloride, cyclobutylaluminum dichloride, ethyl aluminum dibromide, ethly aluminumsesquichloride, ethyl aluminum sesquibromide, dimethyl aluminum bromide,propyl aluminum dichloride, dibutyl aluminum chloride, diethyl aluminumchloride, and the like. If desired, a third component can be employed inorder to increase the stereospecificity of the catalyst and reduce theformation of waxes, oils, and amorphous polymers. Suitable thirdcomponents include the halides of alkali metals, magnesium oxide,aromatic ethers, hydrides of sodium, potassium, and lithium andalcoholates of sodium, potassium, lithium, calcium, magnesium, barium,strontium, aluminum, titanium, and zirconium. In addition, it is oftendesirable to employ tertiary amines and tertiary phosphoramides as thirdcomponents with alkyl aluminum halides.

Catalyst containing a lithium component such as lithium, lithium alkyls,lithium aluminum hydride, lithium hydride and lithium aluminumtetraalkyls in combination with the reduced valency form of thetransition elements from the 4th to the 6th group of the Periodic Tableare preferred for high temperature solutions or melt polymerizationprocedures. These catalysts are particularly effective at temperaturesabove 110 C.

Generally, a mole ratio of activator to metal halide of 0.1:1 to 12:1 issatisfactory in the practice of this invention. Where a third componentis employed, the mole ratios of metal halide to third component of 0.25to 1.0 are generally satisfactory. The concentrations of the catalyst inthe reaction medium can be varied over a wide range. For example,catalyst concentrations of 0.1% or less, up to 3% or more can be used.

The temperature of the two-stage polymerization proc ess can be widelyvaried. However, temperatures ranging from about 0 C. to about 300 C.may generally be employed. With activators other than lithium andlithium compounds it is desirable to use temperatures less than 100 C.In slurry polymerizations at temperatures below 100 C., the inherentviscosities of polymer can be controlled by using hydrogen as asatisfactory chain terminator. In melt or solution polymerization attemperatures above 100 C. the inherent viscosity is controlled by rigidcontrol of the reaction temperature and to a lesser extent bycontrolling the pressure.

A suitable pressure range for the practice of the process of thisinvention include pressures from atmospheric to pressures of about 2,000atmospheres or more. Generally, it is desirable to use pressures inexcess of 15 atmospheres in order to obtain satisfactory rates ofreaction. Higher pressures, for example, 2 to 500 atmospheres may berequired for polymerizations in the absence of a solvent.

The organic vehicle or solvent that can be employed as a reaction mediumin the process of this invention included aliphatic alkanes orcycloalkanes such as propane, pentane, hexane, heptane, cyclohexane andthe like, or hydrogenated aromatic compounds such astetrahydronaphthalene or decahydronaphthalene or a high molecular weightliquid parafiin or mixture of paraffins which are liquid at the reactiontemperature or an aromatic hydrocarbon such as benzene, toluene, xylene,and the like. The nature of the vehicle or solvent is subject toconsiderable variation, but the solvent should be in a liquid form atthe reaction conditions and relatively inert to the reactants andreaction products. Other solvents which can be used include ethylbenzene, isopropyl benzene, ethyl toluene, n-propyl benzene, the diethylbenzenes, mono and dialkyl naphthalenes, n-pentane, noctane, isooctane,methyl cyclohexane, Tetralin, Decalin, mineral spirits and any of theother well-known inert hydrocarbons.

The comonomer which can be copolymerized with polypropylene to form thenovel block copolymers of this invention include any of the Well-knowna-monoolefinic hydrocarbons. However, the preferred comonomers includealiphatic u-monoolefins containing 2 to carbon atoms. Suitablea-monoolefinic hydrocarbons which can be employed include, for example,ethylene, butene-l, pentene, hexene, heptene, decene, styrene, and thelike.

A surprising feature of this invention involved the discovery that inthe formation of propylene-ethylene block copolymers, the polymerizationmust be initiated with propylene and then terminated with ethylene. Whenoperating in this manner, the resulting block copolymer then containsboth propylene and ethylene in the chain, as indicated by infraredanalysis. However, when the polymerization is initiated with ethyleneand then terminated with propylene, no polymerization of the propyleneoccurs, and the polymer chain contains only ethylene.

This invention can be further illustrated by the following examples ofpreferred embodiments thereof although it will be understood that theseexamples are included merely for purposes of illustration and are notintended to limit the scope of the invention unless otherwisespecifically indicated.

EXAMPLE 1 0.60 gram of LiAlH, (.0158 mole) and 2.46 grams of TiCl (.0158mole) slurried in 900 ml. of mineral spirits were charged to a 2-literstirred autoclave. The polymerization was carried out as follows:

Temp., C.

Pressure Time The autoclave was cooled and the polymer washed free ofcatalyst with hot isobutanol. Yield was 320 grams of a -5 weight percentpropylene ethylene block copolymer. The product was characterized by amelt index of 3.67; an inherent viscosity at 145 C. in Tetralin 1.36; aVicat softening point of 131 C.; and a brittleness temperature of --50C. This compares with a brittleness temperature of 20 C. for percentpolypropylene.

EXAMPLE 2 0.75 gram of LiAlH (0.2 mole) and 3.06 grams of TiCl (.02mole) in 900 ml. of mineral spirits were charged to a 2-liter stirredautoclave. The polymerization was carried out as follows:

Time Pressure 2:45 800 p.s.i.g. C3Hfi 2:55 1 700 titanium trichloride.The catalyst suspended in xylene wasfed to the liquid propylene and thepolymerization was carried out at 80 C. and 770 p.s.i.g. using 100 ppm.H to control inherent viscosity. Conversion in the first stage averaged25-30 percent at a catalyst concentration of 0.2 percent.

The polypropylene-catalyst slurry from the first stage was fed to thesecond stage tubular reactor and 4 weight percent ethylene was added andthe polymerization continued at 80 C. and 860 p.s.i.g.

7 From the second stage the polymer slurry in liquid propylene was letdown to a solids-gas separator. The ole- 8 The results of 4 runs usingthe procedure described hereinabove are set forth in the followingtable.

fin was flashed off and sent to a separation unit. The TABLE 2 polymerwas dropped to a wash tank and the catalyst R N 1 4 removal was effectedwith hot isobutanol washing. 0 2 3 Polymer yield per unit of catalystwas 250 and the Pgo i y e ef gig fi f gn ggi -l 10,800 12,100 8,9007.300 polymer contained propylene and ethylene in a 97-3 gfi f M6 (L31M1 weight ratio. The inherent viscosity was 2.25 and the geaetorpressure, atms b 1,270 1,300 1,250 1,500 brittleness temperature was -28C. g gg ggg gggfii 170 167 174 178 First zone bottom. 190 193 191 193EXAMPLE 4 Second zone top 190 192 190 199 1 h E.h f?t ,1"; 55" $28 $38iii n r in yene ee osecon zone 1 0 .Flve addltlonal S We 8 g mProductionrate,lbs.lhr 3,300 4,020 2,170 2,420 dlfierent P? y i 0f p f Te Proce i nherelttvlilsclosity(tetalln,145C.) 2 5 7 2 3 1 2. 43 z eg 11: Green 6 3 8118 in p0 ymer results 0 these runs are Se Brittlenesstemperature,C 26 41 60 60 TABLE 1 Polymerization conditions Weight Molepercent Brittle- Catalyst ratio of Pressure, Comonomer fed comonomerness temp., components components Solvent Temp.,0. p.s.i.g. to 2d stageinpolymer C TiEJ'iiIIIIIIIIIIIIIIIII} 5 1 1 Cyclohexane 160 1,000Ethylene s -50 Diphenyl ether EtsAl Ch TiGh 1/1/1 Mineral spirits so 700do 3 2e 2/1/1 Liq.C H 85 770 Butene-l 7.

' 2/1/0.5 Cyelohexaue 85 400 Hexene-l 2 -22 Al (OPr)a..

LiAlH4 Eiigh 0.l/l/4.9 Mineral spirits 160 1,200 Ethylene 10 53 EXAMPLE5 EXAMPLE 6 As previously indicated, propylene-ethylene polymers withsuperior low temperature properties are produced by carrying out thepolymerization in a 2-zone stirred reactor at elevated pressures andtemperatures. To illustrate this feature of the invention, an elongatedreactor 14 feet long and inches internal diameter separated into twodistinct reaction zones by a centrally located bafile and having astirring mechanism extending through the two reaction zones was used inthe following runs. In the top zone the agitator shaft that extendsthrough the center of the reactor is provided with a single 4- bladedpaddle type agitator at the top of the zone. This type of agitatorarrangement is used to obtain the maximum amount of reaction in thefirst zone with a minimum amount of catalyst. In the second or lowerzone mixing paddles are placed substantially along the entire length ofthe agitator shaft to give a plug flow with a minimum of back mixingfrom the second to the first zone.

Propylene is compressed to 1250 to 1500 atmospheres and fed into the topzone at rates varying from 8,600 to 14,100 pounds per hour. A catalystcomprising 3.2 parts by weight of lithium metal dispersion, 0.17 part byweight lithium aluminum hydride and 14.3 parts by weight of titaniumtrichloride slurried in cyclohexane was fed at rates varying from 0.2 to0.45 pound per hour. The temperature in the first zone is controlled byexternal cooling and by controlling the rate of feed and temperature ofthe incoming propylene. Conversions in the first zone are generallycontrolled at 20-40 percent by controlling the propylene feed rate andthe catalyst concentration employed.

In the second zone ethylene is fed to give propyleneethylene blockcopolymers with superior low temperature brittleness values. Feed ratesfor ethylene varying from 100 to 1000 pounds per hour are typical ofthose employed to give the superior block copolymers of this invention.

Aluminum triethyl (5.0 ml.) and titanium tetrachloride (2.4 ml.) wereadded to 500 ml. of heptane contained in a l-liter 3-neck flask under anitrogen atmosphere. The flask was fitted with a gas inlet tube whichreached to the bottom of the flask, a mechanical stirrer, and abrinecooled reflux condenser. A gas outlet tube led from the top of thecondenser through a mercury bubbler and finally to an ice trapmaintained at -10 to --20 C. The mercury bubbler served to exclude airfrom the reaction vessel and the ice trap was used to determine theamount of solvent swept through the condenser with eflluent monomer gas.

The catalyst mixture was stirred and propylene was introduced throughthe inlet tube at such a rate that little escape through the mercurybubbler. After two hours, 29 grams of propylene had been absorbed. Theintroduction of propylene was stopped and ethylene was introduced for 2hours. Cooling was necessary during this stage to keep the reactiontemperature at or below 60 C.

Methanol (200 ml.) was added to decompose the catalyst and the solidethylene-propylene block copolymer was recovered by filtration. Thesolid was washed free of catalyst with hot methanolic hydrochloric acidand methanol.

The ethylene-propylene block copolymer (mole ratio 2.2/ 0.7) weighed g.and melted at 139-154 C. Properties of the polymer were: melt index,0.028; high pressure melt index, 0.44; density, 0.937; tensile strengthat fracture, 2455 p.s.i., at upper yield, 2175 p.s.i.; percentelongation, 575; stiffness in flexure, 38,600 p.s.i.; Vicat softeningpoint, 1l8.2 C. and a brittle point of 70 C.

EXAMPLE 7 A mixture of 500 ml. of heptane, 10.0 ml. of ethyl aluminumsesquibromide and 10.0 ml. of titanium tetrachloride was prepared in al-liter 3-neck flask. The flask was fitted for propylene polymerizationas described in Example 6. The catalyst mixture was prepared in anitrogen atmosphere as in Example 6.

The reaction mixture was stirred and propylene was introduced beneaththe surface of the liquid. The mixture warmed spontaneously to 5060 andthe rate of propylene fiow was adjusted so that the temperature of thereaction mixture remained between 50 and 60. After 4 hours the weight ofpropylene absorbed was 28 grams.

Introduction of propylene was stopped and ethylene was introduced forthree hours. Occasional cooling was necessary to keep the temperature ofthe reaction mixture between 50 and 60 C.

The crude propylene'ethylene block copolymer was recovered by filtrationand washed free of catalyst with methanolic hydrochloric acid andmethanol. The propylene-ethylene polymer thus obtained weighed 66 gramsand melted at l32145. Properties of the polymer were: high pressure meltindex, 2.86; specific gravity, 0.991; tensile strength at fracture, 2280p.s.i.; Vicat softening point, l05.4 C. and a brittle point of 70 C.

Thus, by the practice of this invention there is provided novelpropylene block copolymers which retain the desirable properties ofcrystalline polypropylene while at the same time being characterized byexcellent low temperature brittle points. The block copolymers can, ofcourse, be used as substitutes for polypropylene in applications wherethis low brittle point is of significance. Such applications wouldinclude their use as wrapping mate rials, fluid containers, fluidconduits or like articles.

Although the invention has been described in considerable detail withreference to certain preferred embodiments thereof, it will beunderstood that variations and modifications can be effected withoutdeparting from the 10 spirit and scope of the invention as describedhereinabove and as defined in the appended claims.

We claim:

1. A solution polymerization process for preparing block copolymerscontaining at least by weight propylene from ethylene and propylenemonomers which comprises first polymerizing'propylene and subsequently amixture of propylene and ethylene in the presence of from about 0.1 toabout 3.0% concentration of catalyst in the reaction medium of acatalyst comprising titanium trichloride and a lithium component at atemperature of at least 133 C., the mole ratio of lithium component totitanium trichloride being 0.1:1 to 12:1.

2. A process according to claim 1 wherein said lithium component is thecomplex reaction product prepared by reacting aluminum alkyl withlithium hydride.

3. A process for preparing block copolymers according to claim 1 whereinsaid lithium component is lithium aluminum hydride.

4. A process according to claim 3 wherein said lithium component is thecomplex reaction product prepared by reacting aluminum alkyl withlithium alkyl.

References Cited UNITED STATES PATENTS 3,200,173 8/1965 Schilling 260878l JOSEPH L. SCHOFER, Primary Examiner S. M. LEVIN, Assistant ExaminerUS. Cl. X.R. 26088.2 R, 93.7

